You're right to ask! It's all about balancing charges. Here's why you need two sodium ions (Na+) for every sulfide ion (S²⁻) in sodium sulfide (Na₂S):

* Sodium (Na) is in Group 1 of the periodic table: This means sodium atoms tend to lose one electron to become positively charged ions (Na⁺).

* Sulfur (S) is in Group 16 of the periodic table: This means sulfur atoms tend to gain two electrons to become negatively charged ions (S²⁻).

To form a neutral compound, the positive and negative charges must balance:

* One sulfide ion (S²⁻) has a charge of -2.

* Two sodium ions (2Na⁺) have a charge of +2.

Therefore, two sodium ions are needed to neutralize the charge of one sulfide ion.

This ensures that the overall charge of the compound is zero, making it stable.